Aktuelle Veranstaltungen

Kolloquium

The microscopic properties of strong-interaction matter under extreme conditions of temperature and density is a topic of great interest.
Matter in equilibrium radiates photons with a thermal spectrum revealing its temperature in the slope of the energy distribution. This is generalized for virtual photons, which materialize after a short time by creation of a pair of charged leptons (dileptons), for which their invariant mass takes the role of the energy as observable. In contrast to the case of photons, their spectral distribution is not affected by a blue (or red) shift. Moreover, dileptons offer the unique opportunity also to directly monitor in-medium electromagnetic spectral functions. Hence, dilepton spectra from strong-interaction medium reflect not only its temperature but also are sensitive to possible effects of a restoration of the spontaneously broken chiral symmetry.
This talk will discuss important experimental results obtained so far at various facilities and the latest theoretical developments on emissivity of matter.

Kolloquium Mathematische Physik

The problem of latency in estimating the Covid-19 replication number

Figuring out how to restart the world's economy without a
resurgence of disease depends on understanding how contagious Covid-19
really is. However, estimates of the basic replication number $R_0$ vary
greatly, with well-respected groups publishing estimates whose 95%
confidence intervals don't even overlap. In this talk I'll go over the basic
SIR and SEIR models of disease spread and present several different ways to
treat the latency period between being exposed and becoming infectious.
Simple SEIR models are unstable; working with a fixed set of data, small
changes to the model can result in large changes to the estimated value of
$R_0$. More realistic models are more complicated and are even less stable.
The upshot is that we know much less about $R_0$ than is generally believed,
and the error bars on the high side are particularly large. Containing the
outbreak for an extended period may be a lot harder than our leaders think.

Seminar Hochenergiephysik

The loss of information in a thermalizing system manifests itself as production of entropy. In relativistic nuclear collisions the final state entropy is proportional to the number of produced particles and therefore the measured particle multiplicities probe the entropy produced during the non-equilibrium evolution of quark-gluon matter. Thanks to the recent understanding of off-equilibrium dynamics using the concept of hydrodynamic attractors, we were able to establish a general relation between the initial state energy and the produced particle multiplicities in high-energy nuclear collisions.
References:
https://doi.org/10.1103/PhysRevLett.123.262301
https://doi.org/10.1103/PhysRevC.100.064903

Seminar Mathematische Physik

Statistics of Extremes in Eigenvalue-counting Staircases

We consider the counting function (“spectral staircase”) for eigenvalues of a random unitary matrix, drawn from the corresponding beta-ensemble. Our goal is to characterize the statistics of maximum deviation of this staircase from its mean slope in a fixed interval, when size of the matrix N >>1. We will show that one-sided extremes can be addressed by exploiting a mapping onto the statistical mechanics of log-correlated random processes and using an extended Fisher-Hartwig conjecture. The resulting statistics exhibits combined features of counting statistics of Fermions with Sutherland-type interaction and extremal statistics of the fractional Brownian motion with Hurst index H = 0. Some of the features are expected to be universal. The talk is based on the paper Fyodorov-Le Doussal arXiv:2001.04135.